.\"	$OpenBSD: SSL_CTX_set_tlsext_servername_callback.3,v 1.4 2019/06/12 09:36:30 schwarze Exp $
.\"	OpenSSL 190b9a03 Jun 28 15:46:13 2017 +0800
.\"	OpenSSL 8c55c461 Mar 29 08:34:37 2017 +1000
.\"
.\" This file was written by Jon Spillett <jon.spillett@oracle.com>
.\" and Paul Yang <yang dot yang at baishancloud dot com>.
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.Dd $Mdocdate: June 12 2019 $
.Dt SSL_CTX_SET_TLSEXT_SERVERNAME_CALLBACK 3
.Os
.Sh NAME
.Nm SSL_CTX_set_tlsext_servername_callback ,
.Nm SSL_CTX_set_tlsext_servername_arg ,
.Nm SSL_get_servername_type ,
.Nm SSL_get_servername ,
.Nm SSL_set_tlsext_host_name
.Nd handle server name indication (SNI)
.Sh SYNOPSIS
.In openssl/ssl.h
.Ft long
.Fo SSL_CTX_set_tlsext_servername_callback
.Fa "SSL_CTX *ctx"
.Fa "int (*cb)(SSL_CTX *, int *, void *)"
.Fc
.Ft long
.Fo SSL_CTX_set_tlsext_servername_arg
.Fa "SSL_CTX *ctx"
.Fa "void *arg"
.Fc
.Ft const char *
.Fo SSL_get_servername
.Fa "const SSL *s"
.Fa "const int type"
.Fc
.Ft int
.Fo SSL_get_servername_type
.Fa "const SSL *s"
.Fc
.Ft int
.Fo SSL_set_tlsext_host_name
.Fa "const SSL *s"
.Fa "const char *name"
.Fc
.Sh DESCRIPTION
.Fn SSL_CTX_set_tlsext_servername_callback
sets the application callback
.Fa cb
used by a server to perform any actions or configuration required based
on the servername extension received in the incoming connection.
When
.Fa cb
is
.Dv NULL ,
SNI is not used.
The
.Fa arg
value is a pointer which is passed to the application callback.
.Pp
.Fn SSL_CTX_set_tlsext_servername_arg
sets a context-specific argument to be passed into the callback for
.Fa ctx .
.Pp
.Fn SSL_set_tlsext_host_name
sets the server name indication ClientHello extension
to contain the value
.Fa name ,
or clears it if
.Fa name
is
.Dv NULL .
The type of server name indication
extension is set to
.Dv TLSEXT_NAMETYPE_host_name
as defined in RFC 3546.
.Pp
All three functions are implemented as macros.
.Pp
The ALPN and SNI callbacks are both executed during Client Hello
processing.
The servername callback is executed first, followed by the ALPN
callback.
.Sh RETURN VALUES
.Fn SSL_CTX_set_tlsext_servername_callback
and
.Fn SSL_CTX_set_tlsext_servername_arg
always return 1 indicating success.
.Pp
.Fn SSL_get_servername
returns a servername extension value of the specified type if provided
in the Client Hello, or
.Dv NULL
otherwise.
.Pp
.Fn SSL_get_servername_type
returns the servername type or -1 if no servername is present.
Currently the only supported type (defined in RFC 3546) is
.Dv TLSEXT_NAMETYPE_host_name .
.Pp
.Fn SSL_set_tlsext_host_name
returns 1 on success or 0 in case of an error.
.Sh SEE ALSO
.Xr ssl 3 ,
.Xr SSL_CTX_callback_ctrl 3 ,
.Xr SSL_CTX_set_alpn_select_cb 3
.Sh HISTORY
These functions first appeared in OpenSSL 0.9.8f
and have been available since
.Ox 4.5 .
